A Head-Up Display (HUD) is a means of projecting information directly into a human's visual field. The HUD was pioneered for military aviation and has since been used in other applications. HUDs are typically used in aircraft to provide pilots with information superimposed onto their forward field of view through the aircraft windshield. The information displayed may be data or symbolic images indicative of flight conditions such as the operating condition of the aircraft, environmental information or guidance information for use in directing the aircraft to its destination. These images are presented in overlying fashion on the pilot's field of view so as not to interfere with the pilot's view of the background scene.
Although HUDs are useful in a variety of applications, there are several problems with conventional HUDs, among which high cost, narrow viewing angles, mechanical constraints, and low contrast of images are of particular concern. Moreover, conventional combiners are either undesirably thick and heavy for most applications, or are thin and undesirably highly curved. The thick combiners often contain a pair of cooperative lens elements, at least one of which includes an embedded spherical surface coated with a spectrally reflecting thin film. The external surfaces of these thick combiners are flat so as to provide an undistorted view of the background scene. Thin combiners, on the other hand, typically employ a pair of spherical external surfaces, one of which carries the spectrally reflecting thin film. Thin combiners thus typically do not provide the necessary undistorted view of the background scene, especially when the combiner is thick enough to be adequately durable.
Thus, it is desirable to provide a method and optical display system for producing images and presenting the images for observation in combination with an observer's visual exterior view of an outside scene, which method and system may solve the foregoing-described problems.